US Deputy Attorney General Rod J. Rosenstein listens to questions at the Wharton School at the University of Pennsylvania on February 21, 2019 in Philadelphia, Pennsylvania. (Photo by AFP)

US Deputy Attorney General Rod Rosenstein, who stirred tensions in Washington by appointing Special Counsel Robert Mueller to investigate President Donald Trump’s ties to Russia, has announced his departure.

Rosenstein made the announcement in a letter addressed to Trump on Monday, writing: “I am grateful to you for the opportunity to serve; for the courtesy and humor you often display in our personal conversations; and for the goals you set in your inaugural address: patriotism, unity, safety, education and prosperity.”

He also used two of the president's campaign slogans to tell him that he helped staff the US Justice department with officials “devoted to the values that make America great” and adding “we always put America first.”

The resignation will take effect on May 11. The White House noted that Trump had already nominated Deputy Transportation Secretary Jeffrey Rosen to replace Rosenstein.

Rosenstein was expected to quit in March but stayed on the job to help Attorney General William Barr redact and publicly release the Mueller report on the 22-month probe, which came out in March and, as Trump insists, “exonerated” him from all charges.

Mueller did not make any determination on whether Trump had obstructed justice in the probe. Rosenstein and Barr made that call after examining the reports and concluding that there was insufficient evidence to support that theory.

“We enforce the law without fear or favor because credible evidence is not partisan,” Rosenstein wrote in the letter.

As a Republican, he often came under fire from Trump and his allies for appointing Mueller to lead an investigation that the president has repeatedly called as a “hoax” and a “witch hunt.”

However, the deputy AG played a key role in weighing the evidence and deciding that Trump should not be charged.

Some unnamed US administration officials have claimed that Rosenstein had tried to mollify Trump in an attempt to save his job.

According to an explosive report by The New York Times last September, Rosenstein had conspired against Trump in 2017 by suggesting to secretly tape Trump and recruit cabinet members to remove him from office under the US Constitution’s 25th Amendment.

Rosenstein said back then that the story was “inaccurate.”

(FILES) In this file photo taken on May 23, 2018 US President Donald Trump stands alongside Rod Rosenstein (R), US Deputy Attorney General, during a roundtable discussion on immigration at Morrelly Homeland Security Center in Bethpage, New York. (Photo by AFP)

However, when Trump asked for an explanation about the report, Rosenstein – teary-eyed according to one account – assured the president that he was on his team and would make sure he is treated fairly in the investigation.

"I give the investigation credibility," Rosenstein was quoted as saying by one administration official who offered their own characterization of the call to the Washington Post. "I can land the plane."

That apparently how he was able to keep his job despite stoking Trump’s ire.

In a speech last week, Rosenstein blasted what he called “mercenary” people who criticize how the Mueller investigation was handled.

“If lawyers cannot prove our case in court, then what we believe is irrelevant,” he said.

Democrats urge Barr to testify before House judiciary panel

Meanwhile, US House Judiciary Committee Chairman Jerrold Nadler said on Monday that Barr was required to answer lawmakers’ questions about the probe this Thursday.

The call came after reports suggested that Barr threatened to skip the session over the aggressive questioning format planned by Democrats.

“We’ve been very clear. Barr has to come. He has to testify. It’s none of the business of a witness to try to dictate to a congressional committee what our procedures for questioning him are,” Nadler told reporters.

“He is supposed to show up on Thursday and we will take whatever action we have to take if he doesn’t,” he added.

Some Democrats argue that the Mueller report, while not conclusive, still provides the ground for a shot at impeaching Trump.